Horselike Fossil From 48 Million Years Ago Preserved While Pregnant

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A 48-million-year-old horselike fossil found near Frankfurt.CreditCreditFranzen et al./Senckenberg Research Institute

By Sindya N. Bhanoo

Oct. 9, 2015

A 48-million-year-old horselike fossil pulled from the rich Messel Pit site near Frankfurt is yielding insights into the evolution of mammalian reproduction. A fetal specimen described in a new study and circled in the photograph at right is the earliest and best-preserved mammalian fetus.

“The question was, is it possible that the placenta was preserved?” said Jens Lorenz Franzen, a retired paleontologist affiliated with the Senckenberg Museum in Frankfurt and one of the study’s authors.

In looking at the fossilized soft tissue, he and his colleagues discovered a preserved placenta, uterus and one broad uterine ligament — evidence, Dr. Franzen said, that the ancient mare had a reproductive system very similar to that of a modern horse.

This means a sophisticated reproductive system was already present in mammals, he said.

The bones of the fetus are also intact except for the skull, which is crushed. The findings appear in the journal PLOS One.

The fetus was first discovered in a fossilized mare found in 2000 by Dr. Franzen and his colleagues. They studied the bones and anatomy of the fetus using scanning electronic microscopy and high-resolution micro-X-ray.

The researchers believe that because the fetus is very developed, the mare died shortly before she would have given birth.

The Eocene freshwater lake of Messel developed within a volcanic crater and, as a result of the eruption, there may have been too much carbon dioxide and too little oxygen, Dr. Franzen said.

A version of this article appears in print on , Section D, Page 4 of the New York edition with the headline: Fossils: 48-Million-Year-Old Fetus and Mother Are Found. Order Reprints | Today’s Paper | Subscribe